Pinched propagation of ion beams for inertial fusion applications

Summary form only given. The authors have discovered a new mechanism for pinched transport of a subrelativistic positive ion beam within a narrow plasma channel formed in a gas at a density of (/spl les/100 mtorr), in a regime where the plasma electrons are collisionless. In the simplest implementation, it may be assumed that the channel is preionized to a charge density greater than that of the beam. The space charge of the beam induces a radial inflow of plasma electrons, which provides space charge neutralization. In this regime, the axial dynamics of the plasma electrons are initially dominated by electrostatic (rather than inductive) forces, which leads to a large axial inflow of plasma electrons from the region in front of the beam. The resulting axial current reinforces the beam current, and generates a strong pinch force at the beam head, which is "frozen in" and persists for the remainder of the beam pulse. The authors are investigating the extent to which this mechanism is effective in an initially underdense plasma channel (or even in the absence of a preionized channel), where the build-up of the plasma channel is due to beam-impact ionization.